The present invention relates to a segmented cylindrical tide-staff system capable of being erected easily at remote areas for dynamic calibration of electronic tide meters and computer models of tides.
The traditional method of coastal hydrographic surveying relies on a tide gauge, which is a device for measurement of tide levels. The tidal height at any place varies with time. The tide gauge records water heights with reference to a recognized datum level known as chart datum (CD), which is a safe low water level in order to maintain the minimum depth useful for transporting a vessel safely to port. The tide gauge records water heights at a selected specified time interval, usually 30 minutes. However, in regions where the tidal height changes rapidly, water heights need to be recorded at much closer time-intervals, say 5 minutes. Traditionally, in the ports all over the world, a human observer records readings from a tide-staff at selected specified time-intervals as described by David. T. Pugh [xe2x80x9cTides, Surges and Mean Sea-Level: A Handbook for Engineers and Scientistsxe2x80x9d, David. T. Pugh, John Wiley and Sons, New York, pp. 1-472 (1987)]. The data recorded is primarily used for operational applications such as hydrographic survey and navigation. The tide-staff readings are also used for periodic chart-datum adjustment of graphical records obtained from float-driven tide gauges as described by H. R. Palmer [xe2x80x9cDescription of Graphical Register of Tides and Windsxe2x80x9d, H. R. Palmer, Philos. Trans. Roy. Soc. London, 121, 209-213 (1831)]. In hydrographic survey, the time-indexed tide is subtracted from time-indexed soundings to provide data for preparation of bathymetric maps, or nautical charts. With advances in nautical charting the application of tide-staff is going to become increasingly important for dynamic calibration of electronic tide gauges and computer models of tides as described by Antony Joseph [In: xe2x80x9cProgress in the Technology of Nautical Chartingxe2x80x9d, Encyclopedia of Microcomputers, Antony Joseph, Marcel Dekker, Inc, New York, Vol. 28, pp. 271-310 (2002)].
Hitherto known systems for tide measurement are shown in FIGS. 1 and 2. FIG. 1 represents a typical design example, showing a conventional tide-staff of the prior art used for tide level measurement with reference to the chart datum (CD), which consists primarily of a single graduated staff [1], which is usually made of wood or any similar material and either driven into the seabed [2] or erected vertically on the side of a jetty-wall. The tide staff reading [3] is in a form visually readable to an average person, and provides precise visual information from a close distance regarding the instantaneous tide level [4] at a given coastal site.
FIG. 2 represents another conventional system of the prior art used for tide level measurement with reference to chart datum (CD), which consists primarily of a single staff [5], which is usually made of iron or a conventional rail pole which is either driven into the seabed [6] or erected vertically on the side of a jetty-wall. Metallic strips [7] are welded to the iron staff [5]. Usually each strip has a total length of 20 cm and is sub-divided into two parts [8] and [9] of length 10 cm each differing in shape to distinguish between these two parts. The adjacent strips of the tide-staff are painted in differing colors to reduce the tide-observer""s burden during tide-staff reading.
Hitherto known systems for tide measurement, describe a tide level recorder that records tide elevations utilizing a vertical free-floating graduated rod-staff, and time-tagging the tide level readings with the use of a chronometer [Jack E. Guth, xe2x80x9cPhoto-Tide Level Recorderxe2x80x9d, U.S. Pat. No. 4,268,839 dated May 19, 1981]. The tide level recorder comprises a vertically oriented graduated rod-staff, which is located on a plastic float to provide it sufficient buoyancy. The rod-staff, which is popularly known as tide-staff, is floated within the confines of a 6-inch diameter plastic vertical cylindrical tube, which functions as a tide-well. A T-shaped junction box attached to the tide-well near its upper end at a point above the highest expected tide level houses a chronometer, an index mark, a time-lapse camera, and a light flash synchronized with the camera. A plastic tube that is mounted vertically above the T-shaped junction box functions as a vertical guide for the rod-staff as it rises and falls with the tide. The tide-well has an orifice near its bottom end to allow the free flow of water in and out as the tide rises and falls. The length and diameter of the tide-well, rod-staff, and rod-staff guide tube, and the height of the index mark and the camera above the orifice are variable and depend on the tidal range, i.e., the extend of vertical swing in water level at the place. The orifice dampens external wave action. The elevation of the rod-staff is relative to the fixed index mark. This index mark is located at a fixed height above the orifice, and its level with reference to a local benchmark can be ascertained from conventional survey techniques. The index mark enables reading the rod-staff graduations as the staff rises and falls with the tide. An automatic time-lapse camera located opposite the index mark enables recording the rod-staff graduation readings and simultaneous time-readings from a chronometer, which is located near the index mark. This arrangement enables relating the tide elevation record to specific times of the day, during which the rod-staff readings are made. An advantage of this device is that it eliminates mechanical errors evident in float-driven gauges operating with the support of counter weights and springs as described by Antony Joseph [xe2x80x9cModern Techniques of Sea Level Measurementxe2x80x9d, Encyclopedia of Microcomputers, Antony Joseph, Marcel Dekker, Inc., New York, Vol. 23, pp. 319-344, (1999)]. Another advantage of this system is that by photo-recording the staff elevation from a fixed camera platform, relative to a fixed reference level, it eliminates the need for the presence of a human tide-staff reader for direct reading of the tide level on the staff. However, a major disadvantage of this device is that it requires a purpose-built structure for erection of the tide-well and related components. Another disadvantage is the requirement of a long tube to guide the tide-staff. Such a long tube is impractical in a location where wind force is appreciable. Yet another disadvantage of this device is that it is not amenable to trouble-free transportation to remote areas and, therefore, not suitable for short-term tide measurements from a multiplicity of remote areas. Still another disadvantage is that the cost of the tide system is very high.
PCT No. PCT/JP91/00610 dated Mar. 4, 1992; and U.S. Pat. No. 5,363,307 dated Nov. 8, 1994 titled xe2x80x9cMeasuring Apparatus Having an Indicator for Displaying Tide or Tidal Current Dataxe2x80x9d by Noriyuki Yoshida and assigned to Furuno Electric Company, Limited, Hyogo, Japan describe an apparatus which displays tide data (among other navigational data) and is installable on a ship. The apparatus comprises a multiplicity of navigational aids including a memory having stored tide data corresponding to ages of the moon in relation to points on the earth, data storing means for storing map data of an area, a ship-position measuring means including one of a Global Positioning System (GPS) receiver for inputting the geographical position (i.e., latitude and longitude) of the ship for specifying a given point of the stored map data, a time-measuring means for inputting the date and time at which the latitude and longitude are calculated, a data searching means for reading relevant tide data that is already stored in the memory based on the calculated latitude and longitude and the date and time; and an indicator for displaying tide data searched by the data searching device. An advantage of this system is that it is useful for hydrographic survey and navigational applications. A disadvantage of this tide display apparatus is its dependence on real-time predicted tide and the absence of tide-measurement to support/validate the predicted values. Another drawback of this apparatus is that the predicted tides stored in the computer memory in the form of Tide Tables are voluminous, as they represent tides data corresponding to the ages of the moon at many points throughout the navigation area. Yet another drawback of this tide display apparatus is that such a predicted Tide Table does not take into account the real situation wherein the tides at a given place can have significant meteorological components such as influences from variable atmospheric pressure and wind.
U.S. Pat. No. 6,295,248 B1 dated Sep. 25, 2001 by Chiaki Nakamura titled xe2x80x9cElectronic Tide Meter, Method for Calculating a High/Low Tide Time and Computer Algorithm for Executing the Samexe2x80x9d and assigned to Seiko Instruments Inc, Japan describe an electronic tide meter wherein the timing of a tide (i.e., when a high tide or a low tide occurs) at a user-selected geographic region and calendar date is calculated based on a computer algorithm using empirically-obtained regional tide data, and the results are displayed. This tide meter comprises an input unit for selecting a geographic region and inputting a calendar date; storing means for storing tide data for each of a plurality of geographic regions; an operating means for determining the tide level at a given time at a given geographic location based on the harmonic constants (representing one of an amplitude and a delay angle in phase) of each basic tidal constituent in the given geographic region determined in accordance with the selected calendar date, and comprising a Fourier series represented by the superposition of the basic constituents obtained from tide level changes in the selected geographic region. In this electronic tide meter a ROM storing means stores an angular speed for each tidal constituent, a correction delay angle and a harmonic constant for each of the plurality of geographic regions that are available for selection by the user. The timing of a tide (i.e., when a high tide or a low tide occurs) is calculated at high speed using a computer algorithm, wherein a whole-day tide level is first determined at certain rough time intervals using a tide level estimation and from the estimated tide data the extreme values (i.e., high tide and low tide values) are derived by an approximation method, based on the change in sign (i.e., a point of inflexion) in the displacement between successive tide levels (i.e., tide-difference changes) in the tide data time-series. Subsequently, a tide level is again determined by a fine time-interval for a limited period near high/low tides. This process yields a better-resolved extreme value of tide corresponding to a proper time-interval representing a given high/low tide phase of the tide, which is of navigational interest. The extreme value as a high tide or low tide level is calculated for a high tide time and low tide time based on a better resolved true points of inflexion, shortening the computer program execution time. An advantage of this system is that it is useful for navigational applications in coastal and estuarine waters. A drawback of this Electronic Tide Display Apparatus is the absence of calibration of the estimated high- and low-tide values against a network of reference-tide-measuring-devices such as tide-staffs that are tied to the local/regional survey benchmark levels, and lack of true measurements to support the predicted high/low tide levels and their true times of occurrence.
U.S. Pat. No. 5,847,567 dated Dec. 8, 1998 by John A. Kielb, Randy J. Longsdorf, Grant B. Edwards, and Donald F. Palan, titled xe2x80x9cMicrowave Level Gauge with Remote Transducerxe2x80x9d, and assigned to Rosemount Inc., Eden describe a level meter for measuring levels of any product including water levels using the principle of microwave echo ranging. The level meter includes a microwave feed-horn directed into the level to be measured, an electronics housing spaced apart from the feed-horn, and a microwave waveguide connecting them. A microwave transducer in the housing couples to the wave-guide and sends and receives microwave signals. A microprocessor in the housing identifies the microwave echoes that are generated and sensed by the microwave transducer. The microprocessor estimates the height of the water level based upon a microwave echo from the water level and another microwave echo from the feed-horn. The microprocessor compensates for the effects of propagation delay through the wave-guide on level measurements with the feed-horn echo and provides an output related to the height of the level that is desired to be measured. An advantage of this system is that the level measurements are performed with reference to the level of the feed-horn. This feed-horn can be leveled against a local benchmark to obtain tide level measurements with reference to the Chart Datum (CD), which is the internationally accepted reference level for tide measurements. A major disadvantage of this system is the requirement of a purpose-built structure and a cabin for protection of its electronics and the display system, thereby operating as a major impediment in its use in remote areas for tide level measurements.
U.S. Pat. No. 6,360,599 B1 dated Mar. 26, 2002 by Ardhendu Gajanan Pathak and Gidugu Ananda Ramadass titled xe2x80x9cDevice for Measuring Liquid Level Preferably Measuring Tide Level in Seaxe2x80x9d and assigned to National Institute of Ocean Technology, Department of Ocean Development, Government of India, Chennai, India describe a device and process for measuring tide levels using the principle of acoustic echo ranging. In this device, an ultrasonic transducer mounted in air and vertically looking downwards directs acoustic energy down towards the water/air interface. The acoustic energy gets reflected back from this interface to the acoustic transducer. The distance between the transducer and the water/air interface is estimated by measuring the time taken between transmission and reception of an energy pulse and from knowledge of velocity of sound in air. From this information the tide level with reference to a known datum can be estimated. This acoustic tide gauge comprises an acoustic transducer or a pair of acoustic transducers for generation and reception of acoustic signals, a mechanical system comprising an acoustic-signal guide-tube, means for calibration, stilling-well and fixtures to erect the system at the site, and an electronic circuit for generation, processing, and displaying of the tide data. Stilling-well is used as a mechanical protection to the acoustic-signal guide-tube against the impact of ocean waves and currents, and also to minimize the effect of water currents and waves on the water level inside the guiding tube. The entire assembly has provisions for fixing the tide gauge to a suitable structure for field-measurements of the tide level. The acoustic transducer/transducer-pair is positioned at the upper end of the acoustic signal-guide-tube having its lower open-end immersed below the lowest tide level. A digital-to-analog converter is used for generation of electrical signals of suitable pulse-width and frequency. A switching circuit isolates the transmitting and receiving signals, and a power amplifier amplifies the received signals. A multiplicity of side-branch tubes provided on the guide tube reflects the sound pulses with a large signal-to-noise ratio. The sounding/guiding tube helps isolate the transducer from other sources of interference, and also confines the ultrasonic beam so that it is directed vertically towards the region of the water surface directly below the acoustic transducer. Further more, the tube produces within it a region of water surface that is substantially damped of waves. The side branches are designed to respond to a specific frequency such that the sound pulse with appropriate center frequency is predominantly reflected by the branch thereby providing a means for in-situ calibration of the acoustic tide gauge by measuring the effective velocity of sound at different portions of the sounding tube. The length of the side-branch, which plays an important role in its effectiveness as a calibrator, is an odd multiple of the quarter wavelength for a given transmission frequency of sound. By the use of properly tuned resonating side branches and signals of different frequencies for calibration and for measurement of the tide level, the limitations existing in in-situ calibration are overcome. The accuracy of tide level measurement depends on the velocity of sound, which varies with temperature gradient of the air column within the sounding tube. The in-situ calibration obviates the basic problem of variation of sound velocity due to temperature gradient in the air within the sounding tube in the axial direction. The length of the said branch tube is determined by a formula that takes into account the wavelength and velocity of the sound signals so as to achieve maximum reflection of acoustic signal. The improved signal-to-noise ratio leads to the improvement in the accuracy of tide level measurement. The diameter of the guide tube is determined by another formula that takes into account the wavelength of the sound signals for realizing plane wave propagation within the guide tube for achieving higher accuracy. An advantage of this system is that the water level measurements are performed with reference to the level of the acoustic transducer. The acoustic head of this transducer can be leveled against a local benchmark to obtain tide level measurements with reference to the internationally accepted reference level for tide measurements, known as Chart Datum (CD). A drawback of this system is that for its efficient full-length in-situ calibration during differing phases of the tide it becomes necessary to attach a series of resonating side-branch tubes of differing lengths at several points on the sounding tube at differing distances from the acoustic head. This makes the system unwieldy. Another disadvantage with this gauge is that it is not possible to achieve the mandatory plane wave propagation condition for the sounding tube for all the differing acoustic transmission frequencies because of a mathematical relationship between the wavelength of the acoustic transmission signal and the diameter of the guiding tube. Still another disadvantage with this gauge is the requirement for a much larger diameter stilling well because of the presence of the protruding resonating side-branches. A further limitation of this tide gauge is the practical difficulty in the installation of the sounding tube locators between the exterior portion of the tubular sounding tube and the interior portion of the stilling-well because of the presence of the resonating side-branches. A major disadvantage of this system is the requirement of a purpose-built structure and a cabin for protection of its electronics and the display system, thereby operating as a major impediment in its use in remote areas for tide level measurements.
Thus there is a need to develop a tide staff system which is easy to transport, facilitates utilization of the services of local manpower for registering tide level readings and eliminates the ambiguity prevalent in the measurements.
The main object of the present invention is to facilitate trouble-free transportation of tide-staffs for tide level measurements from any region including remote areas, by providing a means for partitioning the tide-staff into a multiplicity of desirable smaller segments.
Another object of the present invention is to facilitate easy coupling of any pair of a plurality of separate segments of tide-staffs to achieve any desired height for the full-length tide-staff to suit any given installation environment and any given tidal regime.
Yet another object of the present invention is to provide enhancement of precision in tide level measurements from tide-staffs by providing a multiplicity of protruding tide-indicating arms at regular spatial intervals in an axial direction on their body, thereby eliminating the hitherto prevalent ambiguity in the measurements of tide levels from tide-staffs located at far distances.
Still another object of the present invention is to improve the efficiency of assembly, de-assembly, and packing of the tide-staff system by rendering the tide-indicating arms compact and dismountable.
A further object of the present invention is to simultaneously achieve elegance, ease in mounting, and improving the readability of the tide-indicating arm of a tide-staff by providing the said tide-indicating arm with two mutually orthogonal planes that are drawn from a single strip.
A still further object of the present invention is to facilitate utilization of the services of local manpower for registering tide level readings from remote areas such as coastal villages and fishing areas by providing means for indication of tide reading in more than one language including a vernacular language.
Another object of the present invention is to achieve excellent horizontal azimuthal response to the tide-staff in the presence of flows and waves and to minimize flow/wave-induced piling-up/piling-down effects and wake effects at the tide-staff, by providing a cylindrical shape to the tide-staff segments.